Electrical insulating element such as a distributor cap

ABSTRACT

An insulating element, particularly one which is suitable to accommodate a high-voltage component of a combustion engine ignition system, has a peripheral wall which is composed of closed-cell rigid synthetic plastic foam material to the extent of at least 50 percent its weight. Combustion suppressing and/or reinforcing filler substances may be added to the foam material.

United States Patent 1 Elwert et a1.

11] 3,829,635 Aug. 13, 1974 ELECTRICAL INSULATING ELEMENT SUCH AS ADISTRIBUTOR CAP [75] Inventors: Dietmar Elwert, Esslingen; Gt'itz Gaege,Neustadt, both of Germany [73] Assignee: Robert Bosch GmbH, Stuttgart,

Germany [22] Filed: Sept. 12, 1973 [21] Appl. No.: 396,516

[30] Foreign Application Priority Data Sept. 12, 1972 Germany 2244597[52] US. Cl..... 200/19 WG, 174/138 F, 200/19 DC [51] Int. Cl.... H0lr39/60, HOlh 19/06, HOlb 3/30 [58] Field of Search 174/77 S, 110 F, 137B, 174/138 F, 139; 123/143 C, 146.5 R, 146.5

A, 169 P, 169 PA, 169 PH; 200/19 DC, 19

DR, 19 WG, 168 G; 220/9 F; 339/26, 116 R [56] References Cited UNITEDSTATES PATENTS 2,175,759 10/1939 Olson 200/19 DC UX 2,737,503 3/1956Sprague et a1 174/110 F UX 2,782,251 2/1957 Ebel et a1. 174/110 F UX3,243,504 3/1966 Johnson 174/138 F FOREIGN PATENTS OR APPLICATIONS620,872 5/1961 Canada 174/138 F 700,408 12/1964 Canada... 220/9 F1,593,589 7/1970 France... 220/9 F 1,932,127 l/197l Germany 123/1465 R2,011,242 9/1971 Germany 123/1465 A Primary ExaminerLaramie E. AskinAttorney, Agent, or Firm-Michael S. Striker 5 7 ABSTRACT An insulatingelement, particularly one which is suitable to accommodate ahigh-voltage component of a combustion engine ignition system, has aperipheral wall which is composed of closed-cell rigid synthetic plasticfoam material to the extent of at least 50 percent its weight.Combustion suppressing and/or reinforcing filler substances may be addedto the foam material.

10 Claims, 1 Drawing Figure ELECTRICAL INSULATING ELEMENT SUCH AS ADISTRIBUTOR CAP BACKGROUND OF THE INVENTION This invention relates to anovel article of manufacture, and in particular to a novel insulatingelement.

More specifically, the invention relates to an insulating element suchas a distributor cap which can be used to accommodate a high-voltagecomponent of a combustion engine ignition system.

The invention will be discussed hereafter for the purpose of conveniencein terms of a distributor cap. it should be understood, however, thatthe invention is not limited to such an application and could equallywell be applied to a housing (or part thereof) for an ignition coil, andto still other applications.

Known distributor caps have a peripheral wall of solid cross-sectionmaterial, usually of phenolic or polyester resin. In the course ofnormal use it is inevitable that these caps become heated, just as it isinevitable that at times they will be subsequently subjected to suddenand drastic cooling, e.g., due to atmospheric conditions, due tosplashing of water onto them, or for other reasons. When such suddencooling occurs, a condensation of water droplets takes place at theinner surface of the wall, and this has been found to lead todifficulties. If, namely, these droplets contact dirt particles ornitrous oxides formed by electrical sparking in the interior of the cap,surface leakage paths may develop on the cap, i.e., paths along whichelectrical energy will tend to preferentially creep. This leads toreduction in the electrical insulating capability of the cap and mayfinally result in spark-over. Moreover, acid tends to develop after awhile, which can attack and destroy the material of the cap.

SUMMARY OF THE INVENTION It is an object of the invention to overcomethe disadvantages of the prior art.

More particularly, it is an object of the invention to provide animproved insulating element e.g., a distributor cap wherein thedevelopment of condensation under the aforementioned or similarcircumstances is at least minimized.

In keeping with these objects, and with others which will becomeapparent, we provide an improved insulating element in form of a cuppedbody having a peripheral wall. According to the invention, this wall iscomposed of closed-cell rigid synthetic plastic foam material to theextent of at least 50 percent of its weight.

The air which is entrapped in the cells of the foam material providesfor excellent thermal insulation, so

that even if the body is hot and is suddenly subjected to cooling, thedevelopment of condensate is minimized to a very substantial extent ascompared to the prior art.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE is a partly sectionedperspective view, illustrating one embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the FIGURE, itwill be seen that in the exemplary embodiment the novel insulatingelement, designated in toto with reference numeral 1, is shown as adistributor cap, i.e., as the cap for the housing of a distributor whichforms a part of the ignition system of a combustion engine. Of course,neither the system nor the housing of the distributor have beenillustrated; both are well known per se and not necessary for anunderstanding of the invention.

The element 1 has a peripheral wall 2 which, in this instance where theelement is configurated as a distributor cap, is provided with aplurality of tubular projections 5. The high-voltage lead wires from theignition coil and to the sparkplugs, respectively, are to be introducedthrough these projections into the interior of the hollow cap.

In accordance with the invention, the wall 2 (including the projections5) is composed to the extent of at least 50 percent of its weight from arigid synthetic plastic foam material. It is preferable, however, thatthis percentage be on the order of 65 percent. Since it is desirable tohave good strength even if the wall 2 is relatively thin, we have chosento illustrate that the wall 2 is of so-called rigid structural foam,also known as rigid integral foam. Such foam, which may be ofpolyurethane or polyisocyanurate, to name just two suitable materials,has the characteristic that its porosity is greatest at and near thecenter, so that the wall 2 has a cellular core indicated at 3. Theporosity decreases continuously in direction outwardly away from thecore 3, until the surfaces of the wall 2 are reached where there is noporosity at all, so that at these surfaces the wall is provided withnon-porous skins 4. This type of foam provides high rigidity andstrength at relatively low wall thickness, and prevents the entry ofdirt,

moisture and other contaminants into the cell structure of the wall 2.Moreover, the wall 2 also has good resistance to attack by acids.

Where there is a danger of inflammation, e.g, if the wall element isused as a distributor cap and subjected to fire hazards associated witha combustion engine, it is advisable to include in the material of thewall a flame-suppressing or combustion-suppressing substance. Aluminumoxide hydrate (Al O '30-35% H O) has been found suitable for thispurpose. Such a substance may be admixed with the foam to the extent ofbetween 10 and 50 percent by weight of the wall 2, preferably about 35percent.

If necessary, the rigidity of the wall 2 can be further increased byadmixing with the foam a filler material, for example kaolin, talcum ormica. There, again, the filler substance may amount to between 10 and 50percent, preferably about 35 percent by weight of the wall 2 It will beappreciated that it is possible to add a flameor combustion-suppressionsubstance as well as filler material. In that case, however, the twosubstances together must not amount to more than at most 50 percent byweight of the wall 2, and preferably should not exceed 35 percent.

The foam material of wall 2 not only serves as an eff cient thermalinsulator, but also as a fully satisfactory electrical insulator. Thiseliminates the need for a separate layer of electrical insulatingmaterial and, in conjunction with the low expense of the foam material,substantially reduces the manufacturing costs of the novel element.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofapplications differing from the types described above.

While the invention has been illustrated and described as embodied in adistributor cap, it is not intended to be limited to the details shown,since various modifications and structural changes may be made withoutdeparting in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for var ious applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. in a distributor for a motor vehicle, in combination, a distributormechanism; a distributor cap having a circumferential wall at leastpartially surrounding said distributor mechanism, an end wallsubstantially closing an end of said circumferential wall, and aplurality of tubular wall portions projecting from said end wall foraccommodating electric input and output leads, said distributor capbeing composed of a first reinforcing skin facing exteriorly of saiddistributor cap, a second reinforcing skin facing interiorly of saiddistributor cap, said skins being impermeable to fluids, and a cellularcore integral with and intermediate said first and second skins forelectrically and thermally insulating the former from the latter,whereby condensation of water vapor on said second skin is effectivelyprevented.

2. A distributor cap comprising a peripheral wall including acircumferential wall portion, an end wall portion substantially closingone end of said circumferential wall portion, and a plurality of tubularwall portions projecting from said end wall portion, said peripheralwall being composed of closed-cell rigid synthetic plastic structuralfoam material to the extent of at least 50 percent of its weight andhaving-a cellular core and non-cellular impermeable outer exposedreinforcing skins.

3. An element as defined in claim 2, wherein said foam material includesa plurality of closed cells, the size of said cells gradually decreasingfrom a point substantially midway of said skins in direction towards thelatter.

4. A distributor cap as defined in claim 2, wherein said structural foamis a polyurethane foam.

5. A distributor cap as defined in claim 2, wherein said structural foamis a polyisocyanurate foam.-

6. A distributor cap as defined in claim 2, wherein said peripheral wallfurther includes a combustionsuppressing substance.

7. A distributor cap as defined in claim 6, wherein said substance isaluminum oxide hydrate.

8. A distributor cap as defined in claim 6, wherein said peripheral walladditionally includes a filler substance for increasing the rigidity ofsaid foam material.

9. A distributor cap as defined in claim 2, wherein said peripheral wallfurther includes a filler substance for increasing the rigidity of saidfoam material.

10. A distributor cap as defined in claim 9, wherein said fillersubstance is kaolin.

2. A distributor cap comprising a peripheral wall including acircumferential wall portion, an end wall portion substantially closingone end of said circumferential wall portion, and a plurality of tubularwall portions projecting from said end wall portion, said peripheralwall being composed of closed-cell rigid synthetic plastic structuralfoam material to the extent of at least 50 percent of its weight andhaving a cellular core and non-cellular impermeable outer exposedreinforcing skins.
 3. An element as defined in claim 2, wherein saidfoam material includes a plurality of closed cells, the size of saidcells gradually decreasing from a point substantially midway of saidskins in direction towards the latter.
 4. A distributor cap as definedin claim 2, wherein said structural foam is a polyurethane foam.
 5. Adistributor cap as defined in claim 2, wherein said structural foam is apolyisocyanurate foam.
 6. A distributor cap as defined in claim 2,wherein said peripheral wall further includes a combustion-suppressingsubstance.
 7. A distributor cap as defined in claim 6, wherein saidsubstance is aluminum oxide hydrate.
 8. A distributor cap as defined inclaim 6, wherein said peripheral wall additionally includes a fillersubstance for increasing the rigidity of said foam material.
 9. Adistributor cap as defined in claim 2, wherein said peripheral wallfurther includes a filler substance for increasing the rigidity of saidfoam material.
 10. A distributor cap as defined in claim 9, wherein saidfiller substance is kaolin.